The Radiation Pattern of Reflector Impulse Radiating Antennas: Early-Time Response

We generate here an approximation to the step response of reflector Impulse Radiating Antennas (IRAs) in the Eand H-planes. These step responses are then convolved with the derivative of the driving voltage to find the radiated fields. This allows a determination of the radiation pattern of reflector IRAs. < L Introduction The transient radiation from a planar aperture field distribution was developed in [1]. This o was fbrther specialized to two-wire apertures in [2], but only on boresight. The off-boresight fields created by a two-wire aperture were never developed. We do so in this paper. The results we provide here are valid for a wide variety of practical cases. Although it is true that these results are valid only at high impedances, this is not very conilning in practice, because at low impedances one incurs significant feed blockage anyway, Furthermore, our expressions are derived explicitly only for round wire feeds, But since the feed arms are relatively thin at high impedances, the specific shape of the feed should not matter very much. Thus, the results developed here are usefil for other feed arm shapes, such as coplanar plates and curved plates [3]. We begin by providing a review of the static fields between two wires. This is the field we find in the aperture of a reflector IRA. Next, we radiate this field with a step-fimction driving voltage. Expressions are provided for the E-plane and H-plane fields (pattern) created when the aperture fields are turned on suddenly. Furthermore, we demonstrate that on boresight our results are consistent with earlier results calculated by contour integration. Finally, we convolve the step response with the derivative of a typical driving voltage, in order to get the response to a realistic driving voltage. With this inforrnatio~ we can calculate a gain and antenna patte~ according to the definitions of [4].